PCI: provide stub pci_domain_nr function for !CONFIG_PCI configs

Allows the new PCI domain aware DRM code to compile on m68k.
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

include/linux/pci.h

@@ -1214,6 +1214,9 @@ static inline struct pci_dev *pci_get_bus_and_slot(unsigned int bus,
 						unsigned int devfn)
 { return NULL; }
 
+static inline int pci_domain_nr(struct pci_bus *bus)
+{ return 0; }
+
 #define dev_is_pci(d) (false)
 #define dev_is_pf(d) (false)
 #define dev_num_vf(d) (0)